SOBRE LA METODOLOGÍA

Second Edition Paul B. Moore

The following is an excerpt from Chapter Two

To gain any appreciation at all of the effect one alloy or another may have on the quality of a bullet or the cost of the final product, a basic understanding of the kinds of materials one is likely to encounter in the bullet casting business is in order.

It is not the purpose of this chapter to champion one alloy over another concerning its application as a bullet alloy, but to clear up misconceptions about the

analytical composition of the materials available to the bullet caster. All compositions listed hereafter are extrapolated nominal chemistries determined by the atomic absorption and classical wet analytical

techniques. The performance of any given alloy in a single firearm is subject to a host of variables and only one of these is the analytical composition of the bullet itself. The only true test is to try it and see if it works for your application.

Any discussion involving the analytical composition of scrap alloys most certainly has to start with the most common source of salvaged lead alloy, the wheel weight. There is probably not a bullet caster in the country who has not at one time or another melted a pot of dirty wheel weights, skimmed off the clips, dirt and dross and then cast bullets with the remaining alloy. Some bullet casters have more success with wheel weights than others do.

Wheel weights have probably been used by bullet casters since very shortly after the first wheel was balanced with them. Today, wheel weights are manufactured in two distinct compositions, which if mixed at random, have a significant effect on the weight and hardness of the bullets cast with them, undoubtedly contributing at times to the woes of the bullet caster. Analytically, the most common wheel weight is made of three percent antimonial lead with the following nominal composition:

antimony3.00 percent; tin 0.29 percent; arsenic 0.14 percent; copper 0.05 percent; bismuth 0.025 percent maximum; nickel .002 percent maximum; zinc .001 percent maximum; sulfur .001 percent maximum and the remainder lead. The residual elements of bismuth, silver, iron, nickel, zinc and sulfur are essentially the same for almost all the compositions discussed. Consequently, they will be ignored unless they are present in significant amounts.

To make matters more difficult for bullet casters, there is a second reasonably

common composition of wheel weights, consisting of antimony 0.68 percent; tin 0.017 percent; arsenic 0.08 percent, copper 0.05 percent and the remainder is lead.

Unfortunately, there is no efficient way to separate these two different alloys. And obviously, mixing these two quite different alloys in varieties of unknown proportions can have significant effects on the composition and thus the weight of the bullets cast from the resulting mixtures. With the three percent antimony wheel weight containing more than four times as much hardener as the 0.68 percent-antimony wheel weight, the physical properties of the mixture change as the composition changes. The only effective way to handle the problem is to melt as large a batch as possible and cast it into ingots for later remelting into to cast bullets. This would minimize small lot

variations in composition and at least produce bullets of consistent weight and hardness while the original batch lasts.

The words "Type Metal" in bullet casting circles, almost universally refers to linotype or eutectic alloy. Unfortunately, "Type Metal" is in reality a broad name applied to five categories of material used in manufacture of type, each with three to five sub-

classifications. Since there are seventeen of these different type metals, Chart I details the nominal analytical composition of each. Fortunately for the bullet caster, linotype or eutectic alloy is the most commonly available. That is if any can be found at all.

Note that the foundry type contains a relatively large concentration of copper. As far as is known, no one has completed and extensive test of this material as a bullet metal, so its use to the caster of bullets is unknown. In all probability the copper would tend to come out of the solution in the form of high melting inter-metallic compound with tin and antimony, thus impairing castability.

Lead shot, though a single classification of material is in reality many different alloys constructed ti impart different physical qualities to the pellet. Buckshot is normally soft or pure lead. Chilled or drop shot is normally a 0.50 percent antimonial lead. Chart II lists specific analyses. Note in the analyses two elements that make these alloys unique. First, none contain tin. Second, both chilled and hard shot contain significant quantities of metallic arsenic. Arsenic metal is introduced into the alloy to reduce surface tension and thereby produce rounded pellets. Tin is withheld because it would negate the effects of arsenic.

For the bullet caster concentrations of arsenic greater than about 0.30 percent can create problems - not from the possible toxic effects as might be expected but because relatively large amounts of arsenic cause metal to shrink unevenly, greatly increasing the probability of cracked bullets, especially in the grease grooves. There is a remote possibility that upon firing or loading a cracked bullet, a portion of the bullet would remain in the barrel - creating a potential bore obstruction for the next shot- or a piece could break off and fall back into the case, creating a potential high pressure situation. The probability of these things occurring is unknown. However, the potential results are severe enough that any lead shot that is to be used as bullet casting material should be diluted enough to reduce the arsenic content to below 0.30 percent.

Lead pipe is commonly thought of as being made of pure lead. Although this idea is not entirely correct, it is not far from the truth. Most lead pipe is made from an alloy called chemical lead, which has a nominal composition of 0.05 percent copper and the balance lead. There is also a significant amount of antimonial lead pipe containing from three to ten percent antimony as indicated by Chart III. The single peculiarity of lead pipe, other than its analytical variability, results from the fact it is extruded, not cast. This peculiarity can deceive the bullet caster. When a lead alloy is extruded, it work softens, sometimes substantially, giving the impression that the material is somewhat softer than it really is. This peculiarity should be of special interest to commercial casters and muzzle loader shooters, since work softened material that is remelted and cast into round ball is considerably harder than in its original extruded form. Always check the hardness of the bullet or ball itself, never the raw material in its original form.

Bearing or Babbitt alloys are used primarily by the automotive and related industries for rod, cam and crankshaft bearings. There are now hundreds of different

compositions of such bearings, but most of these are slight variations of twelve major categories. Chart IV details these twelve major categories. Some of them would make fine bullet alloys, like number nine and others would be terrible, number three for example. Unfortunately, there is no practical method of determining exactly which of

these alloys a scrap supply consists of - only by direct chemical analysis. But if you have found a Babbitt alloy that makes good bullets, and they shoot well, there is no reason not to use it for bullets.

Sheet lead is normally used as a sound insulator by construction companies for buildings. Bullet casters may find this material in and around buildings being demolished, or naturally at scrap yards. There are four basic compositions of sheet lead and these are listed in Chart V. The vast majority of this material is

manufactured from chemical lead but significant amounts are produced from four percent and six percent antimonial lead. Sheet lead is not cast but rather rolled on rolling mills. Therefore, like lead pipe the antimonial leads work soften and when melted and cast into bullets become harder than the material in its original form. Strontium lead sheet should be avoided if found and identified because the alloy contains aluminum which increases surface tension of the alloy, inhibiting casting. Ingot lead can normally be purchased through plumbing supply houses, and contrary to popular belief, it is usually not pure lead. Most lead distributed by plumbing

suppliers has an antimony content of approximately 0.30 percent with the balance lead. This material would make good base metal for alloying with other materials, but muzzle loaders cannot count on it being pure. If it causes no problem, then keep using it; but if there is a problem, the antimony content will be the culprit.

Many houses today have lead alloy roof flashings for vents. This material is composed of about 0.30 to 0.50 percent antimony, the rest being lead. This material would also make a good base material for blending with other materials to yield harder bullet metal. Demolished houses are possible sources.

Telephone companies use cable lead to insulate their underground wires from the elements. This material appears to be completely soft. However as an extruded product, it has the same properties of those materials already discussed. It contains 0.50 percent antimo9ny and is about forty percent harder than pure lead after it is cast into bullets. Scrap yards are the most likely source for cable lead, which makes a fine case for further alloying. Note one thing about cable lead: the telephone

companies coat the inside of the lead cable sheathing with grease and paper to make it weather hardy. Scrap cable lead therefore smokes like the dickens and will smoke up your house if you don’t remove the grease and the paper before melting the lead. There are hundreds of types of cast solders and Chart VI lists the nominal chemistries of the thirteen most common. Most of these can be purchased in one ingot size or another through local solder distributors or plumbing supply houses. Every bullet caster is familiar with 50/50 solder bar, yet not everyone knows that that the first figure always refers to the tin content and the second figure to the lead content. Of course, to every rule it seems there must be an exception and solders are not exempt - alloy 95/5 contains ninety-five percent tin and five percent antimony, with no

significant lead content at all.

Hundreds of alloys are used in the manufacture of batteries. Unlike solder, battery lead is very poor for bullet metal. Of course, it is possible to salvage the terminals, but the plates are an entirely different matter. Manufacturers recover the metal in plates through a smelting process where temperatures reach from eighteen hundred to twenty four hundred degrees Fahrenheit. To make matters even more interesting, battery manufacturers have begun in recent years to use calcium and strontium lead alloys in manufacturing battery plates. It is possible in attemting to melt calcium and strontium lead battery plates, to liberate arsine or stibnite gas - which could be fatal. Avoid batteries as a source for bullet metal.

Deep alloying and refining is a subject that will be discussed in another chapter. However a cursory treatment here is warranted. Alloying is a word used to refer to mixing two or more elements or materials to produce a third material that is somehow more desirable for some purpose than either of the original materials. For instance, if one were to mix equal portions of cable lead and linotype, the resulting lead would contain approximately 6.25 percent antimony and 2.00 percent tin. This is a useful alloy in that it does not waste the high tin and antimony content of the linotype, yet still has the hardness and castability needed for most applications. Another benefit is that scrap lead cable is probably much less expensive than linotype and alloying the two together will double the number of quality cast bullets that could be produced using linotype alone and at a significantly lower cost.

Another possibility would be equal portions of wheel weights and linotype, producing an alloy with approximately 7.5 percent antimony and 2.14 percent tin. This alloy should be slightly harder than the cable and linotype alloy and somewhat less expensive yet.

Another combination that is frequently written about is 50/50 solder bar alloyed with wheel weights. Any addition of more than two percent tin to the wheel weights (or any other alloy used for bullet casting) would be wasteful as well as expensive. Plus, the additional castability and hardness provided by higher concentrations of tin would be negligible. It is even possible to get by with less than two percent tin depending on the bullet mold and style. Try it and see.

Whenever lead alloys are melted, fluxed and skimmed, the material has been refined. Additionally, anytime anything is present that is undesirable, regardless of

concentration, then that material needs to be refined. Deep refining will be discussed in another chapter, however, for the present let’s say that the easiest and most efficient way to remove undesirable elements is to dilute them down to a low enough level to make their concentration insignificant.

Question: What are the best bullet alloys?

Anwswer: Alloys will vary depending on the application. More

information can be found in the excerpt from the HANDBOOK OF COMMERCIAL BULLET CASTING located in the book section. Magma test casts their molds using an alloy of 6% Antimony, 2% Tin and 92% Lead.

Question: Why do my bullets sometimes look wrinkled?

Answer: The mold isn’t hot enough or there is oil residue in the mold

cavity. Just drop the wrinkled bullets back in the pot and recast.

Question: What is antimony and why do I need it to cast a bullet?

Answer: Antimony is a metallic chemical element (Sb). It is used to

harden other metals. When two or more metals are mixed together they are referred to as an alloy. The typical bullet alloy is made of lead, with antimony added for hardness and tin added for ease in casting.

Question: What is the correct casting temperature for bullet alloy?

Answer: The best casting temperature for any given alloy is the

coolest temperature that gives you the best bullets. Every alloy has its own "best" temperature based on the percentages of component

metals. Temperature is also affected by air temperature and humidity, and the accuracy of your temperature controls. Temperature is further influenced by the heat absorption/retention of the mold itself. Rule of thumb: Use the coolest temperature that makes good bullets, in that mold, from that particular alloy, on that day. This trial and error method applies to either hand casting or machine casting.

Question: What determines the accuracy of a cast bullet? Answer: There is a casters' legend that claims the base of the bullet

must be smooth and properly formed. Field work has disproved this theory. Instead, tests have proven the single most important factor in determining a bullet's accuracy is the relationship of bullet diameter to the bore. The bullet should be .0005" to .001" larger than the bore. Other than that you must also consider the following:

ƒ Selecting the correct alloy for the type of bullet to be cast. ƒ Loading the cases to the proper maximum overall length of the

finished cartridge and the cartridge fits the firearm properly.

ƒ Being aware of the work-soften factor as you size bullets. Alloyed

lead becomes softer as it is swaged. Size as soon as possible after casting.

ƒ Making certain the alloy remains clean.

ƒ Use the correct antimony and tin ratio for the expected velocity of

the bullet. As a rule of thumb: 3% antimony for low velocity; 6% antimony and 2% tin for medium to high velocity; 12% antimony and 4% tin for highest velocity bullets. Pure lead should be used for muzzle loader balls. If 3% antimony doesn't cast well in your particular set of molds, try adding 2% tin to it in the form of plumber's fifty-fifty solder bar. The added tin does not increase hardness significantly but does improve the castability of the alloy.

ƒ Lead base bullets harden or soften with age. Lead-tin-antimony

alloys slowly harden over the course of about three weeks, and then their final hardness stabilizes. The age hardening quality can affect the ultimate quality and accuracy of the bullet. Tin-lead alloys either do not harden at all or age-soften depending on what specific alloy was used.

ƒ An ineffective lubricant can also cause accuracy problems. Not all

lubricants work with all bullets, in all firearms under all

conditions. For a general dependable lubricant, try Magma lube.

Question: What causes "fins" on a bullet?

Answer: Fins are caused by mold blocks that are not closing properly.

If you suspect a mold block problem, remove the mold and inspect it for foreign matter and machine burs. Clean the mold carefully but thoroughly. Pay attention to the small grooves cut into the mold face leading to the bullet cavities. These are vent groves and their purpose is to allow air to escape from the mold cavity when the molten lead is poured in. These grooves are typically .0015" to .002" deep. If these grooves become plugged with any foreign matter, the bullets cast in the mold's cavity will not fill out properly.

Question: I want to experiment with different alloys but I'm not sure where to start.

Answer: Complete information on calculations is available in The

Handbook of Commercial Bullet Casting. In the chapter discussing

alloying and refining, a compositional breakdown of various metal types is listed as well as the simple equation you will need for calculating the ratio of material to another. If you don't want to bother with the math, use the Alloy Program. This is the computer program that automatically computes the cost and materials used in the book. The program is available on 5.25 or 3.5 disk for IBM compatibles. It can be run with Windows like any other DOS based program.

Question: Which bullet is best for paper targets; a wad cutter or a semi-wad cutter?

Answer: That depends on the result you are looking for. A wad cutter

will punch a perfectly round hole in a paper target. This is important in